This invention generally relates to a permanent magnet design that is especially useful for permanent magnet motors.
A variety of permanent magnet electric motors have been used for various purposes. A variety of challenges and difficulties must be overcome when designing such motors.
One example of a difficulty associated with permanent magnet motors is trying to overcome flux disturbances that result as the rotor moves relative to the stator. In electric induction motors, when rotor conductors move past stator slots, which have partial or full slot openings facing the air gap, disturbances result. The disturbance usually produces acoustic noise, vibration and torque pulsations. One attempt at minimizing this effect is to skew the rotor by arranging the magnets in a staggered or skewed arrangement. In another attempt the stator conductors and their slots are skewed. While this does serve to attenuate the flux disturbances, there still are difficulties to overcome. Placing and mounting skewed magnetic blocks on a cylindrical rotor is not easily accomplished. Similarly, a relatively difficult mounting process is required to accomplish the desired results in a permanent magnet linear motor. This is especially true when trying to mount magnets on the secondary portion of the motor assembly. It is especially difficult to place skewed magnets within rotors or secondaries having embedded magnets.
There is a need for a more versatile arrangement that will accommodate skewed magnets on a rotor portion of a motor assembly. Moreover, there is a need for a less cumbersome and less expensive way of accomplishing flux disturbance attenuation in permanent magnet motors. This invention addresses those needs and avoids the shortcomings and drawbacks associated with the prior art described above.
In general terms, this invention is a permanent magnet that has a body and a magnetic field that is skewed relative to the body. A permanent magnet designed according to this invention has a central axis of the body. At least one surface on the magnet is not aligned with the body axis. When a permanent magnet designed according to this invention is used in a motor assembly, the magnet body mounting surface is aligned with the rotor axis while the skewed surfaces are not aligned with the rotor axis.
A motor assembly including magnets designed according to this invention does not experience the flux disturbances that occur in other motor designs. Moreover, a motor assembly designed according to this invention is much more economical to manufacture compared to previous arrangements.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.